This is a common problem that I also faced. Initially I was going to ceiling mount the QS8s on a rear "knee wall", about 5 ft behind the listening area at about 135 degrees from straight ahead. At least they'd be symmetrical with respect to the room center line.
However I did some listening tests with the QS8s on ladders and compared it to approx 90 degree locations. To my ear I liked the 90 degree location a lot better.
I used QSS stands holding QS8s at about 90 degrees L/R from the lisening position. One is against the wall and the other is out in the room. Fortunately I was re-carpeting at the time so got special flat speaker cable and ran it under the carpet pad. The visible speaker wire is covered with Radio Shack flexible black conduit. It's secured to the QSS base, so if kicked the wire won't pull over the QSS tower. It's a darkly decorated, dedicated HT room, so it doesn't look bad. There's enough slack to reposition the QS8 to a better location if children are about, etc.
In general the QS8s are tolerant of positioning. My advice is try them out temporarily on ladders, have two friends hold them, etc. It's possible having one on the wall and the other on the ceiling would be just fine for you.
